Problem with Spirit rover's steering reappears
MISSION CONTROL STATUS REPORT
Posted: October 21, 2004
A problem that affects the steering on NASA's Mars Exploration Rover Spirit has recurred after disappearing for nearly two weeks.
Engineers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., are working to fully understand the intermittent problem and then implement operational work-arounds. Meanwhile, Spirit successfully steered and drove 3.67 meters (12 feet) on Oct. 17.
Rover engineers are also analyzing a positive development on Spirit's twin, Opportunity: a sustained boost in power generation by Opportunity's solar panels.
Both rovers have successfully completed their three-month primary missions and their first mission extensions. They began second extensions of their missions on Oct. 1.
Rover engineers refrained from driving Spirit for five days after an Oct. 1 malfunction of a system that prevents wheels from being jostled in unwanted directions while driving. Each of the front and rear wheels of the rover has a motor called a steering actuator. It sets the direction in which the wheel is headed. The steering actuators are different from the motors that make the wheels roll, and hold the wheel in a specific direction while driving. A relay used in turning these steering actuators on and off is the likely cause of the intermittent nature of the anomaly.
The relay operates Spirit's right-front and left-rear wheels concurrently, and did not operate as commanded on Oct. 1. Subsequent testing showed no trace of the problem, and on Oct. 7, the rover steered successfully and drove about 2 meters (7 feet), putting it in position to examine a layered rock called "Tetl" for several days. However, the anomaly occurred again on Oct. 13, and the problem appeared intermittently in tests later last week.
"We are continuing tests on Spirit and in our testbed here at JPL," said Jim Erickson, Mars Exploration Rover project manager at JPL. One possible work-around would be to deliberately blow a fuse controlling the relay, disabling the brake action of the steering actuators. The rovers could be operated without that feature. "The only change might be driving in shorter steps when the rover is in rugged terrain," Erickson said.
Spirit has driven a total of 3,647 meters (2.27 miles) since landing, more than six times the distance set as a goal for the mission. Its current target is a layered rock called "Uchben" in the "Columbia Hills." Opportunity has driven 1,619 meters (just over a mile). Its latest stop is a lumpy boulder dubbed "Wopmay" inside "Endurance Crater."
The daily power supply for each rover comes from 1.3 square meters (14 square feet) of solar panels converting sunlight into electricity. Just after the landings in January, the output was about 900 watt-hours per day for each rover -- enough to run a 100-watt bulb for nine hours. As anticipated, output gradually declined due to dust buildup and the martian seasonal change with fewer hours of sunlight and a lower angle of the Sun in the sky. By July, Spirit's daily output had declined to about 400 watt-hours per day. It has been between 400 and 500 watt-hours per day for most of the past two months.
Opportunity, closer to Mars' equator and with the advantage of a sunward-facing tilt as it explored inside the southern half of a crater, maintained an output level between 500 and 600 watt-hours per day in June, July and August. Since early September, the amount of electricity from Opportunity's solar panels has increased markedly and unexpectedly, to more than 700 watt-hours per day, a level not seen since the first 10 weeks of the mission.
"We've been surprised but pleased to see this increase," said Erickson, "The team is evaluating ways to determine which of a few different theories is the best explanation."
Possible explanations under consideration include the action of wind removing some dust from the solar panels or the action of frost causing dust to clump. "We seem to have had several substantial cleanings of the solar panels," Erickson said.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA's Science Mission Directorate, Washington.
| Democracy in Orbit: Chiao to Vote in Space |
10.21.04 | |
 Of the millions of American citizens eligible to vote this Election Day (Nov. 2), there's only one who won't be on the planet. But Expedition 10 Commander Leroy Chiao isn't letting that little detail keep him from casting his ballot. Image left:Chiao gives a "thumbs up" on the way to the launch pad in Kazakhstan on October 13. Photo Credit: NASA/Bill Ingalls. Click for larger image Even though he'll be floating around the Earth 230 miles up on the International Space Station, Chiao is not too far from the polls to stand up and be counted, thanks to a bill passed in 1997 by Texas legislators. The bill sets up a technical procedure for astronauts -- nearly all of whom live in Houston -- to vote from space. (And here's a bonus bit of presidential trivia: The bill was signed by the then-governor of Texas, George W. Bush.) Here's how it will work. An electronic ballot, generated by the Galveston County Clerk's office, will be emailed to Chaio's secure account at NASA's Johnson Space Center. Mission Control Center there will transfer the email to the Station using a high-speed modem via satellite, the same way they send all astronauts e-mails to the Station. Then, Chiao will cast his vote and use a secure e-mail connection to send his ballot back to the clerk's office to be recorded. It will be the first vote ever to be cast in a presidential election from space. But Chiao's democracy in orbit doesn't end there.
2.9 Mb Quicktime | 2.7 Mb Windows Media "A few years ago, the Texas State Legislature passed a bill allowing astronauts to vote from space," Chiao said from aboard the Space Station. "Why did they go to so much trouble for just a few people? Because voting is each citizen's most basic, yet most powerful tool for participating in America's cherished right to choose its leaders." Chiao is only a few days into a six-month mission as commander of the tenth crew of the International Space Station. His Expedition 10 crewmate is Russian Cosmonaut Salizhan Sharipov. Returning Expedition 9 crewmember Mike Fincke will be voting by absentee ballot, because he'll be in Russia for post-flight activities on Election Day. |
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